1. Field of the Invention
The present invention relates to an etchant composition used to etch an indium oxide layer including indium zinc oxide (IZO) or indium tin oxide (ITO) that is formed on a substrate of an electronic device.
2. Description of the Background
IZO may be prepared by mixing indium oxide (In2O3) and zinc oxide (ZnO) in a suitable ratio. ITO may be prepared by mixing indium oxide (In2O3) and tin oxide (SnO3) in a suitable ratio.
A layer of ITO or IZO may serve as a transparent electrode and may be formed by several process steps. In particular, ITO or IZO is first deposited on a glass substrate by a known method such as sputtering to form an indium oxide layer, and a photoresist is then coated on the indium oxide layer. Next, the photoresist is exposed and developed to form a desired pattern. The indium oxide layer is then selectively etched through the photoresist pattern, resulting in the formation of a transparent electrode.
The indium oxide layer typically exhibits prominent chemical resistance and serves as an obstacle during an etching process which makes the process quite difficult.
Conventional etchants for etching an indium oxide layer include an aqua regia-based etchant (HCl+HNO3) disclosed in Korean Patent Publication No. 96-2903, an etchant containing one of hydrochloric acid, weak acid, and alcohol-based compound disclosed in Korean Patent Publication No. 97-65685, a ferric chloride-based etchant (FeCl3+HCl) disclosed in U.S. Pat. No. 5,456,795, an etchant containing oxalic acid, oxalate, and aluminum chloride as main components disclosed in Korean Patent Publication No. 2000-0017470, and an etchant containing hydrogen iodides (HI) and ferric chloride (FeCl3) disclosed in U.S. Pat. No. 5,340,491.
The aqua regia-based etchant has a low price but it damages the profile of an etching pattern and its compositions vary easily due to volatility of hydrochloric acid and nitric acid.
The ferric chloride-based etchant has the same problems as the aqua regia-based etchant since its main component is hydrochloric acid.
The etchant that includes oxalic acid shows good etching efficiency but it is apt to be crystallized since it shows poor solubility at a low temperature.
The etchant that includes HI is advantageous because it exhibits a higher etch rate and causes very little damage to the pattern profile. Nevertheless, this etchant is difficult to use in process lines because it is too expensive, has strong toxic properties, and is corrosive.
In addition, since most known etchants in the art have higher chemical activity, they may erode adjacent layers made of metals that have lower chemical resistance, such as Mo, Al, and Cr, for example. Accordingly, electronic devices such as thin-film transistor liquid crystal displays (TFT-LCD) that have multi-layered structures have limitations on the compositions of the multi-layered structures.
Furthermore, the etchants that contain hydrochloric acid generate fumes that may cause air pollution. For this reason, proper exhaust facilities are required and much caution is required when operating the production lines.